1. Field of the Invention
The present invention relates to a sheet treating apparatus, particularly to a sheet treating apparatus, for example, for aligning and stitching a sheet bundle, and an image forming apparatus provided with this sheet treating apparatus.
2. Related Background Art
For a conventional sheet stitching apparatus (sheet treating apparatus) for stitching the end of a sheet bundle formed by aligning a plurality of sheets, the following apparatus is general.
A sheet on which an image is formed by a main body of an image forming apparatus is discharged from a predetermined discharge port of the image forming apparatus main body in a predetermined timing. The sheet is accepted from an inlet port of a sheet stitching apparatus, nipped by a sheet conveying roller, and conveyed to a sheet stitching portion. Thereafter, a plurality of sheets are stacked on a sheet stacking portion for stacking the sheets to be stitched. The stacked sheets are aligned in a sheet conveying direction and in a sheet width direction orthogonal to the conveying direction before subjected to sheet stitching. After a sheet bundle is aligned, sheet stitching means performs a designated stitching operation of the sheet bundle. Additionally, the sheet stitching comprises performing the stitching in a position where the sheet bundle is aligned, or conveying the aligned sheet bundle in toto to a sheet stitching position and performing the sheet stitching in the position.
An aligning operation usually comprises thrusting a leading end of the sheet onto an abutment portion disposed on the leading end side of the sheet conveying direction with a belt or a roller, a paddle or another rotating member, a pressing member constituted to be reciprocatable in the sheet conveying direction for abutting against a trailing end of the sheet to press the leading end of the sheet onto the abutment portion, and the like so that the sheet conveying direction is aligned. Furthermore, the alignment of the sheet width direction orthogonal to the sheet conveying direction is performed by alignment plates which can reciprocate in the sheet width direction and operate so as to hold the sheets stacked on the sheet stacking portion from both sides.
The stitched sheet bundle is discharged onto a sheet discharge tray of the sheet treating apparatus disposed in a position where a user can take the sheet bundle by discharging means such as a sheet bundle conveying roller pair, a belt member and a conveying member for abutting against the sheet bundle to push out the sheet bundle.
By repeating the above-described operation for the necessary number of sheet bundles, the sheet bundles are successively discharged, and stacked onto the sheet discharge tray.
In the above-described conventional example, however, the following improvements are demanded.
In the sheet treating apparatus for performing a predetermined treatment on the sheet, a pretreatment sheet which is provided with the formed image and conveyed to the sheet treating apparatus needs to be accurately aligned. For this, the sheet stacking portion is positioned for temporarily stacking the conveyed sheet before the predetermined treating operation is performed, and the aligning operation is performed in the position.
However, in some cases, a sufficient alignment cannot be performed because of the sheet conveying state, sheet type, and other factors.
For example, in case that ends (leading end and trailing end) of the sheet in the conveying direction of the sheet are curled, when the sheet is to be aligned in the sheet conveying direction, the end fails to correctly abut against the abutment portion, and the aligning property in the sheet conveying direction is deteriorated.
Moreover, when the sheet is discharged to the sheet stacking portion, the sheet largely deviates in a direction different from the discharge direction due to a discharging energy, and in some cases the sheet deviates from a position on the sheet stacking portion where an appropriate aligning operation can be performed.
In order to solve these problems, it is considered that an uncurling member for removing the sheet curl during sheet conveying, or a large-sized aligning device be disposed, but such member enlarges the sheet treating apparatus, and further increases manufacture costs, which disagrees with user""s demands for small size, space saving and cost reduction on the image forming apparatus and the sheet treating apparatus.
The present invention has been developed to solve the above-described problems, and an object thereof is to provide a sheet treating apparatus which prevents the sheet conveyed to sheet stacking means from deviating and which can securely perform sheet aligning, stitching, and another sheet treating even in a curled sheet, and an image forming apparatus provided with the sheet treating apparatus. The sheet treating apparatus comprises discharging means for conveying and discharging a sheet with an image formed thereon; sheet stacking means on which the sheet discharged by the discharging means is stacked; an abutment reference member disposed on the side of a sheet leading end of a direction in which the sheet is discharged onto the sheet stacking means from the discharging means, against which abutment reference member a leading end of the sheet discharged onto the sheet stacking means abuts; and an urging member disposed on the side of a sheet trailing end of the direction in which the sheet is discharged onto the sheet stacking means from the discharging means, for urging the sheet discharged from the discharging means toward the abutment reference member.